Process of electro lyzing crude salts of aluminium



(No Mddel.)

C. M. HALL.

PROCESS OF ELEGTROLYZING CRUDE SALTS 0F ALUMINIUM Patented Apr. 2, 1889.

ummwmx UNITED STATE PATENT OFFICE.

CHARLES M. HAIL, OF OllERlilN, ()lllt).

PROCESS'OFWELECTROLYZING CRUDE SALTS OF ALUMINIUM.

SPECIFICATION forming part of Letters Patent No. 400,666, dated April'2, 1889.

Application filed August 17. 1888. $erial No. 282,955. (No specimens.

T0 all-whom it nmy colbccrn:

Be it known that-- I, CHARLES M. llALL, a

citizen of the United States, residing at Oberlin, in the county ofIiorain and State of Ohio, have invented or discovered certain nevi-"anduseful Improvements in theManufacture of Aluminium by Electrolysis ofitsFused Salts, of which improvements thev followingis a specification.

In applications filed July 9, 1886, and February 2, 1887, and seriallynumbered 207,601v

and 226,206, respectively, I have described and claimed processes forthe reduction of tion of the fiuoride'of lithiunnand in the processdescribed in application, Serial No. 226,206 I employed a bath formed ofthe fluo rides of potassium and aluminium, (represented by the formula KAI F with or without the addition of the fluoride of lithium; The saltsforming "either of the above-mentioned baths are placed in a suitableyessel,

preferably one formed of. metal and-lined with carbon, and thensubjected tosu flicient heat to fuse them and .form a homoge-nous bath.Electrodes formed of carbon orany suitablemetal and connectedto.oppositc poles of a dynamo-elcctric machine are then placed i'iithebath, or the conmining-vessel may be employed as thencgativeelectrode.The alumina is now added to the bath, and

being dissolved aluminium is reduced at the negative electrode, andbeing fused'byihe heat of the bath sinks to the bottom of the vesscl,the oxygen being liberated atthcposiium produced. The formation of theblack the form of bauxite, anhydrous oxide of compound, which occurssooner in the bath composed of the fluorides of sodium and aluminiumthan in thatcomposcd of the fluorides of potassium and aluminium,necessitates a com paratiwrl y f requent renewal of the bath.

The obj ect of theinventio'u described herein is to provide a bathwherein the objections heretofore mentioned do not obtain, and which canbe used continuously without changes or renewal, exceptto supply lossoccurring. from evaporation.

In the accompanying drawings forming a part of this specification isshown a construction of apparatus applicable for carrying out myimproved process.

In the practice of the present invention I form an electrolyte or'bathof the fluorides of calcium, sodium, and aluminium, the fluorides ofcalcium and sodium being obtained in the form of fluor-spar andcryolite,respect.-

ively, and the fluoride of aluminium being obtained by saturatinghydrated alumina (Alllq with hydrofluoric acid. The compound resultingfrom the mint ure of the abovementioned fluorides, which is represent-edapproximately by the formula Na Al Ffi erably formed of metal and linedwith pure carbon, for the purpose of preventing the admixture of anyforeign material with the bath or with the aluminium when reduced. Thevessel 1. is placed in a furnace, 2, and sub jected to sufficient heatto fuse the materials placed therein. 'lwo clcctrmles, 3 and 4, of anysuitable material, prefi-u'ably carbon ,when pure aluminium is desired,and connected to the positive and negative poles of any suit-, ablegenerator of electricity, preferably a dynamo-electric machine, areplaced in thef used bath; or, if desired, the carbon-lined vessel may beemployed as the negative electrode, as represented in dotted lines.-Alumina in aluminium, or any othcr suitable form of alumina, preferablythe pure anhydrous oxidc A1 0 artificially prepared, is then placed inthe bath, and, being dissolved thereby, aluminium is reduced by theaction of electric current at the negative electrode and being fused bythe heat of the bath sinks down to the bottom of the vessel, the bathbeing of aless specific gravity than the aluminium.

.CaAl F placed in a suitable vcssel,1, pref- This difference in specificgravityis an important feature of my process, as the superineumbeut bathserves to protect the aluminium from oxidation. The oxygen of thealumina is liberated by the action of the electric current at thepositive electrode, and, when the latter is formed of carbon, combinestherewith and escapes in the form of carbonic oxide 0) or carbonic acid((0 As the aluminium is reduced, more alumina is added, so that the bathmay be maintained in a saturated condition with the fused alumina.'lheaddition of more alumina than can be dissolved at one time is notdetrimental, provided the bath is not chilled, as such excess will sinkto the bottom and be taken up by the bath, as required.

The proportions of the materials employed in forming the bath orelectrolyte are approximately as follows: Fluoride of calcium, twohundred and thirty-four parts; cryolite, the double fluoride (Na Al Ffour hundred and twenty-one parts, and fluoride of aluminium, eighthundred and forty-five parts, by weight. These proportions can, however,be widely varied without materially changing the efficiency of the bath.During the reduction of the aluminium the positive electrode, whenformed of carbon, is slowly consumed and must be renewed from time totime; but the bath or electrolyte remains unchanged for a long time. Intime, however, a partial clogging occurs, which, however, does notrender the bath wholly ineffective, but does necessitate an increase inthe electro-motive force of the reducing-current, the resistance of thebath being increased in proportion to the degree to which the bathbecomes clogged,

thereby increasing the cost of reduction. In order to entirely preventany clogging of the bath, I add approximately three or four per cent.(more or less) of calcium chloride to the bath or electrolytehereinbefore described. As the addition of the calcium chlorideprevents, as stated, any clogging or increase of resistance in the bath,it can be used continuously without renewals or any additions, exceptsuch as may be needed to replace loss by evaporation, and withoutincreasing the electro-motive force of the reducing-current; and,further, the addition of the calcium chloride enables each atom ofcarbon of the positive electrode to take up two atoms of oxygen, formingcarbonic acid, (C0 thereby reducing the amount of carbon consumed inproportion to the amount'of aluminium produced. The calcium chloridebeing quite volatile is subject to loss faster than the rest of thebath, and must be renewed occasionally on this account.

In red ucing aluminium; as above described, I prefer to employ anelectric current of about six volts electro-motive force; but theelectromotive force can be varied within large limits.

I claim herein as my invention-- 1. As an improvement in the art ofmanufacturing aluminium, the method herein described, which eonsists infusing a combination of the fluoride of aluminium, the fluoride ofcalcium, and the fluoride of sodium, adding alumina to the bath soformed, and then passing-a current of electricity through the fusedmass, substantially as set forth.

2. As an improvement in the art of manufacturing aluminium, the methodherein described, which consists in fusing a combina-,

tion of the fluoride of aluminium, the fluoride of calcium, the fluorideof sodium, and the chloride of calcium, adding alumina to the bath soformed, and then passing a current of electricity through the fusedmass, substantially as set forth.

In testimony whereof I have hereunto set. my hand. I

CHARLES M. HALL. \V itnesses:

W. B. CORWIN, DARWIN S. WoLco'rr.

